Proliferative retinopathies were studied biochemically in an experimental model, using newbown and young dogs and cats, and eyeballs of other animals available in a local slaughterhouse. Studies involved the purification of angiogenic factor(s) and elucidation of the vasoproliferation mechanism. During this stage of study, we are focusing on improvements in bioassay techniques for quantitation of angiogenic activity, and on purification of angiogenic factor from vitreous and retina. We have partially purified the angiogenic factor(s), which has a molecular weight of less than 2000 and is extremely potent in promoting vasoproliferation in chick embryo chorioallantoic membrane. Results from this study also indicate that the isolated angiogenic factor is a naturally occurring substance and may be responsible for both normal vascularization and abnormal neovascularization in retina. The factor is not liberated by the ischemic retina as previously suggested.